The present invention relates to isocyanurates, and to compositions useful in the preparation of polymeric isocyanurates. More particularly, the present invention relates to isocyanurates which when cured have excellent physical properties at high temperatures.
The expression "vinylidene group" when used in this application means the group characterized by the formula: ##STR2## wherein the two free valence bonds are not both connected to the same carbon atom.
The expression "aromatic polyisocyanate" when used in this application means a compound containing at least 2 isocyanate groups attached directly to the carbon atom of an aromatic ring.
The expression "isocyanurate" means a compound containing the structure: ##STR3##
The products of this invention may be generally classified as thermoset resins. The prior art thermoset resins lack one or more important physical properties which would be desirable in their use. It is an object of this invention to prepare curable thermosetting compositions which combine excellent viscosity control at low as well as high dissolved solids concentrations; which are easily handled for laminate preparation; which may be blended with copper salts to yield a low exotherm on cure to prevent bubbling and warpage; which have a broad range of solubility in vinylidene monomers with which it is copolymerizable; which when cured form thermoset resins which exhibit good corrosion resistance in a variety of media, including water, acid and alkali; and which yield cured resins with superior stiffness and rigidity and excellent retention of physical properties at elevated temperatures.
It has been discovered that all of these properties are now achievable with the products of this invention and that it is also possible to combine these desirable properties with fire retardance and low smoke. The versatility of these resin systems makes possible the preparation of a wide range of products with properties superior to general purpose polyester resins and isophthalic resins, as well as other specialty vinyl ester resins.
The resins of this invention are further characterized by a very high level of aromatic and cyclic character which are derived both from the aromatic polyisocyanate and from the isocyanurate ring. This high degree of aromatic and cyclic character is believed by contribute substantially to the improved thermal stability and to the stiffness and rigidity of the products prepared therefrom. The combination of these highly aromatic and cyclic compositions with acrylate and methacrylate unsaturation makes possible a rapid curing system with excellent retention of physical properties not readily achievable from prior art products. It also allows for a versatile solubility in a variety of comonomers with which the products of this invention will copolymerize. The products of this invention have a molecular weight range that allows the proper solution viscosity (about 100 to about 1000 cps) for good handling and lay-up when making laminates. Products of this invention have a viscosity above 1000 cps may also be prepared for use in applications requiring high viscosity. The products of this invention can be prepared at low solids concentration and still exhibit the proper viscosity for good handling.
The isocyanurates of this invention are isocyanurates of urethanes of an aromatic polyisocyanate and at least one vinylidene carbonyl oxy alkanol characterized by one of the following formulae: ##STR4## wherein R.sub.1 is hydrogen or an alkyl group containing from 1 to 4 carbon atoms, R2 is hydrogen, alkyl containing from 1 to 12 carbon atoms, or a chlorinated, brominated, or fluorinated alkyl group containing from 1 to 12 carbon atoms, R3 is hydrogen, alkyl containing from 1 to 12 carbon atoms, or a chlorinated, brominated, or fluorinated alkyl group containing from 1 to 12 carbon atoms, R4 is hydrogen, methyl or ethyl, and n is from one to four, with the proviso that R2 and R3 on adjacent carbon atoms are not both alkyl or chlorinated, brominated, or fluorinated alkyl, that is at least one of R2 and R3 must be hydrogen. In order to obtain resins having the excellent combination of high temperature physical properties provided by the present invention, it is essential that the resin be prepared from an unsaturated isocyanurate composition wherein at least a major amount of the isocyanurate moieties are based on one or more vinylidene carbonyl oxy alkanols defined above. Illustrative examples of such alkanols include; hydroxypropyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxyethyl acrylate, pentaerythritol triacylate, pentaerythritol trimethacrylate, and diacrylates and dimethacrylates of trimethol propane, trimethylol ethane, trimethylol methane, and glycerol. A preferred group of vinylidene carbonyl oxy alkanols include hydroxypropyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxyethgyl acrylate, and blends thereof. Another preferred group of such alkanols are blends of polyfunctional acrylates or methacrylates such as pentaerythritol triacrylate, pentaerythritol trimethacrylate, and mixtures thereof, with one or more monofunctional acrylates or methacrylates such as hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, and hydroxyethyl methacrylate.
While the isocyanurates of this invention must contain moieties derived from one of the vinylidene carbonyl oxy alkanols defined above, the moieties derived from an aromatic polyisocyanate may be based on any trimerizable aromatic polyisocyanate. In fact, any trimerizable aromatic polyisocyanate which is conventionally used in the art for the preparation of isocyanurates may be used to prepare the isocyanurate compositions of the present invention. For example, the aromatic polyisocyanate may or may not contain ethylenic unsaturation and it may be monomeric or polymeric. The only requirements are that the aromatic polyisocyanate contain at least two aromatic isocyanate groups, be trimerizable, and be free of any groups which interfere with the trimerization of isocyanate groups or which interfere in the reaction of an isocyanate group with a hydroxyl group. Illustrative examples of aromatic polyisocyanates which are particularly useful in the preparation of isocyanurate compositions of this invention include: 2,4-tolylene diisocyanate; 2,6-tolylene diisocyanate; m-phenylene diisocyanate; p-phenylene diisocyanate; 1,5-naphthalene diisocyanate; 4,4'-diphenyl ether diisocyanate; 4,4',4"-triphenylmethane triisocyanate; 2,4,4'-triisocyanatodiphenylmethane; 2,2',4-triisocyanato diphenyl; 4,4'-diphenylmethane diisocyanate; 4,4'-benzophenone diisocyanate; 2,2-bis(4-isocyanatophenyl)propane; 1,4-naphthalene diisocyanate; 4-methoxy-1,3-phenylene diisocyanate; 4-chloro-1,3-phenylenediisocyanate; 4-bromo-1,3-phenylene diisocyanate; 4-ethoxy-1,3-phenylene diisocyanate; 2,4'-diisocyanatodiphenyl ether; 4,4'-diisocyanatodiphenyl; 9,10-anthracene diisocyanate; 4,6-dimethyl-1,3-phenylene diisocyanate; 4,4'-diisocyanatodibenzyl; 3,3'-dimethyl-4,4'-diisocyanatodiphenylmethane; 3,3'-dimethyl-4,4'-diisocyanatodiphenyl; 3,3'-dimethoxy-4,4'-diisocyanatodiphenyl; 1,8-naphthalene diisocyanate; 2,4,6-tolylene triisocyanate; 2,4,4'-triisocyanatodiphenyl ether, diphenylmethane diisocyanate, polymethylene polyphenylene polyisocyanate available under the trademarks Mondur and Papi, having a functionality of 2.1 to 2.7; 1,3-xylene 4,6-diisocyanate; aromatic isocyanate terminated polyurethanes; and aromatic isocyanate terminated pre-polymers of polyesters. Although it is preferred to use all aromatic polyisocyanate, small amounts of an aliphatic polyisocyanate, for example, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, or alpha,alpha'-diisocyanato-p-xylene, may be used in combination with the aromatic polyisocyanate.
Small amounts of monoisocyanates may be present to modify the structure of the isocyanurate formed. The use of small amounts of monoisocyanates improves elongation and gives better control of the reaction to prevent gelation, particularly when triisocyanates are used. The amount of monisocyanate used is usually selected to furnish a ratio of isocyanate groups originating with monoisocyanates to isocyanate groups originating with polyisocyanate of not more than 0.5, and preferably a ratio of not more than about 0.3. Typical examples of monoisocyanates which may be used include p-tolylisocyanate, phenylisocyanate, and n-butylisocyanate. Preferred polyisocyanates are 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, polymethylene polyphenylene polyisocyanates having an average functionality of 2.1 to 2.7, and mixtures thereof.
The unsaturated isocyanurate compositions of this invention are a mixture of urethane containing unsaturated isocyanurates of an aromatic polyisocyanate and at least one vinylidene carbonyl oxy alkanol characterized by one of the above formulae. The exact structure of each component of these compositions and the precise amount of each component present in the compositions are not known. However, it is known that the essential components of the isocyanurate compositions of this invention contain vinyl groups, ester groups, urethane groups and isocyanurate groups. It is also believed that these groups are linked together in the following sequence: vinylester-urethane-isocyanate ring. Although applicants do not wish to be bound to a particular structural formula, it is believed that preferred unsaturated isocyanurate compositions of this invention are a mixture of isocyanurates characterized by the following formulae: EQU R"(R').sub.x+1
wherein R" is an aromatic radical free of a group which is reactive with an isocyanate group and is obtained by removing the isocyanate groups from an aromatic polyisocyanate,
wherein x is an integer which is one less than the number of isocyanate groups present in the polyisocyanate,
wherein each R' is independently ##STR5## with the proviso that at least one R' is ##STR6## and with the proviso that each terminal R' is ##STR7## wherein R'" is a monovalent organic radical having the formula obtained by removing a hydroxyl group from a vinylidene carbonyl oxy alkanol characterized by formulae (1) thru (5) recited above and where each R"" is independently--H or ##STR8## and
wherein the total number of isocyanurate rings in each molecule is less than about 400.
It is apparent from the foregoing formula that the isocyanurates of this invention may also be described as esters of carboxy amino phenyl isocyanurates and vinylidene carbonyl oxy alkanols. These esters contain one or more isocyanurate ring per molecule or, as is usually the case, comprise a mixture of ester containing one isocyanurate ring per molecule with ester containing more than one isocyanurate ring per molecule. These esters may or may not contain allophanate groups. Prior to curing, the solid isocyanurates of this invention are fusible, that is, they exhibit a softening point by the Ring and Ball method described in the A.S.T.M. Designation E28-58T.
Preferred isocyanurate compositions of this invention exhibit characteristic infra-red (IR) peaks at 5.75-6 microns (carbonyl), 6.1-6.35 microns (amidic hydrogen), 6.9-7.2 microns (isocyanurate), and 10.15-10.85 microns (vinyl). A preferred class of isocyanurates have IR peaks at 5.8-5.95 microns, 6.2-6.3 microns, 7.00-7.15 microns, and 10.2-10.75 microns. Preferred isocyanurates of this invention which are prepared with toluene diisocyanate and hydroxylpropyl methacrylate exhibit IR peaks in styrene at about 5.85 microns, about 6.23 microns, about 7.1 microns, and about 10.6 microns.
The isocyanurate compositions of this invention which are styrene solutions of isocyanurates based on toluene diisocyanate and hydroxylpropyl methacrylate may be further characterized within experimental error by the following nuclear magnetic resonance (NMR) signals at: 9.6.+-.0.2, 8.8.+-.0.2, 7.50, 7.48, 7.44, 7.41, 7.36, 7.33, 7.29, 7.26, 6.79, 6.71, 6.57, 5.93, 5.91, 5.70, 5.69, 5.33, 5.31, and 5.19. The isocyanurate compositions of this invention which contain allophanate groups will give an additional NMR signal at 10.6.+-.0.2. All NMR measurements recited in this application were determined by proton magnetic resonance spectral measurements on a Varian CFT-20 spectrometer operating at 79.54 MHz (nominal 80 MHz) at 30.degree. C. Dimethyl sulfoxide was used as solvent. The results are quoted as chemical shifts in parts per million (ppm) relative to tetramethyl silane as internal standard.
The unsaturated isocyanurate compositions of this invention are all soluble in at least one of the following free-radical polymerizable ethylenically unsaturated monomers: divinylbenzene, styrene, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, butyl acrylate, butyl methacrylate, tetramethylene glycol diacrylate, trimethylol propane triacrylate, pentaerythritol triacrylate, neopentyl glycol diacrylate, 1,3-butylene glycol diacrylate, 2,3-dibromopropyl acrylate, 2,3-dibromopropyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, chlorostyrene, acrylonitrile, vinylidene chloride, vinyl acetate, vinyl stearate, vinyltolylene, hexanediol diacrylate, hexanediol dimethacrylate, and mixtures thereof. The term "soluble" means that at least two grams of the isocyanurate composition can be dissolved in 100 grams of at least one of the above-listed ethylenically unsaturated monomers at 25.degree. C.
The ethylenically unsaturated isocyanurate compositions of this invention may be prepared by reacting an aromatic polyisocyanate with one of the above-described vinylidene carbonyl oxy alkanols to form an isocyanate containing urethane and then trimerizing the isocyanate-containing urethane until essentially all isocyanate groups have reacted to form the ethylenically unsaturated isocyanurate composition of this invention. It will be understood, of course, that the resulting isocyanate composition may contain some residual isocyanate groups. Other methods of preparing the isocyanurates will be apparent to those skilled in this art.
More particularly, the isocyanurate compositions of this invention may be prepared by the method described in patent application Ser. No. 819,353, entitled "ESTERS OF CARBOXY AMINO PHENYL ISOCYANURATES AND VINYLIDENE CARBONYL OXY ALKANOLS" filed by Dr. Kenneth H. Markiewitz on July 27, 1977, the disclosure of which is hereby incorporated into the present application by reference. Briefly, this process is a two-step process which comprises a first step of reacting an aromatic polyisocyanate with a vinylidene carbonyl oxy alkanol in the presence of a copper salt, such as cupric acetate, to form an isocyanate-containing urethane and a second step of trimerizing the isocyanate-containing urethane in the presence of an isocyanate trimerization catalyst to form the ethylenically unsaturated isocyanurate composition of this invention.
The solution viscosity of the unsaturated isocyanurates of this invention can be varied over a wide range by adjusting the stoichiometry of the aromatic polyisocyanates and vinylidene carbonyl oxy alcohols employed in their synthesis and/or the temperature of the trimerization. Thus by varying the degree of the excess isocyanate groups compared to hydroxyl groups it is possible to adjust the formation of high molecular weight species and solution viscosities at a fixed concentration. Increasing the excess of isocyanate groups compared to hydroxyl groups favors higher molecular weight species and therefore higher viscosities, conversely lowering the excess isocyanate groups compared to hydroxyl groups favors lower molecular weight species and therefore lower viscosities. By appropriate adjustment of this excess a curable resin solution of the desired viscosity can be obtained. This may be done by experiment, realizing that higher solids concentration, and higher reaction temperatures also lead to resins of increased molecular weight and solution viscosity. The converse of this is also true. The excess of moles of NCO groups compared to moles of --OH per mole of polyisocyanate should be kept in the range from about 0.75 to about 1.6, and preferably from about 0.8 to about 1.4. In a solution comprising equal parts of solvent and a mixture of hydroxypropylmethacrylate and toluene diisocyanate, the excess of moles of NCO groups for laminate applications is preferably from about 0.8 to about 1.05.
The expression "excess of moles of NCO groups compared to moles of --OH per mole of polyisocyanate" means the excess of moles of NCO groups is equal to the moles of NCO used minus the moles of --OH used divided by the moles of polyisocyanate used.
The solution viscosity is also increased as the temperature used in the trimerization reaction increases, but this is not as important a variable as the excess of isocyanate groups compared to hydroxyl groups. However, the trimerization temperature is most often maintained from about 0.degree. C. to about 95.degree. C., since the trimerization reaction is slow at lower temperature and higher temperature may cause the vinylidene group to polymerize prematurely. A preferred trimerization temperature is from about 50.degree. C. to about 90.degree. C.
The particular trimerization temperature chosen will control the amount of allophanate remaining in the isocyanate composition. In general, the higher the temperature the lower the allophanate content. Allophanate-free isocyanurate may be prepared by conducting the trimerization at a temperature of above about 85.degree. C. Allophanate-free isocyanurates may be prepared also by heating an allophanate-containing isocyanurate product of this invention to a temperature of, preferably, from about 85.degree. C. to about 95.degree. C. in the presence of a trimerization catalyst. Higher temperatures may be employed subject to the stability of the resin system. The isocyanurate products of this invention usually have an allophanate content sufficient to give an allophanate to urethane stoichiometric ratio of from about 0 to 0.7, and preferably from about 0 to 0.2, as determined by NMR measurements.
The characteristic of an allophanate free resin are (1) less evolution of gases when a peroxide and resin is heated and (2) longer shelf life of the uncured resin in the presence of unpromoted peroxides. Allophanate free resins may be prepared for the preparation of thick laminates in order to minimize gas evolution at elevated temperatures.
It will be readily apparent to one skilled in the art that some isocyanurate compositions of this invention may contain as a by-product urethanes which do not contain an isocyanurate ring. These urethanes may be formed by the reaction of all the isocyanate groups of the polyisocyanate used with hydroxyl groups from the vinylidene carbonyl oxy alkanol used. For example, isocyanurate composition of this invention made with tolylene triisocyanate and hydroxypropyl methacrylate may contain as a by-product the diurethane of one mole of tolylene diisocyanate and two moles of hydroxypropyl methacrylate. These urethanes may be characterized by the formula EQU (R.sub.a)(R.sub.b).sub.k
where R.sub.a is an aromatic radical free of a group which is reactive with an isocyanate group and is obtained by removing the isocyanate groups from an aromatic polyisocyanate, k is an integer which is equal to the number of isocyanate groups present in the polyisocyanate, and R.sub.b is ##STR9## where R.sub.c is a monovalent organic radical having the formula obtained by removing a hydroxyl group from a vinylidene carbonyl oxy alkanol characterized by formula (1) thru (5) recited above. The amount of such urethanes present in the compositions of this invention will depend mainly on the trimerization temperature and on the hydroxyl to isocyanate ratio used to prepare the isocyanurate composition. In general, the higher the trimerization temperature and/or the higher the ratio of hydroxyl groups to isocyanate groups, the higher will be the amount of such urethanes in the final product. In some cases the amount of such urethanes may amount to up to 65% by weight but more usually in the range of 10% to 50% by weight of the total composition.
Generally, as the solid content of the resin system decreases so does the solution viscosity, and to compensate for this reduction in viscosity which may make preparation of laminates a difficult task, the amount of high molecular weight polyisocyanurate structure is increased by increasing the excess of isocyanate groups to hydroxyl groups. The amount of these species may also be controlled by adjusting the trimerization temperature.
The following Table I illustrates ways to obtain vinylidene carbonyl oxy alkanol containing urethane isocyanurate solutions over a broad viscosity range. Although the table refers to the reaction products from hydroxypropylmethacrylate (HPMA) and toluene diisocyanate (TDI) dissolved in styrene, those skilled in the art will understand that similar relationships hold true for other solvent systems using other polyisocyanates or vinylidene alcohols. The examples in Table I illustrate the effect of the three important reaction parameters on the viscosity of the final product. Examples F and G as well as H and I show the effect of trimerization temperature on the viscosity of the final product. Examples D and F and J and L illustrate the effect of concentration on the viscosity, whereas, examples B and C, E, F, and I and also J and K demonstrate the effect of the molar excess of NCO groups compared to hydroxyl groups per mole of polyisocyanate, on the viscosity of the final product. All reactions listed in the table were carried to completion, i.e., the residual isocyanate content was essentially zero. Additional viscosity control may be achieved also by stopping the reaction short of completion as can be done in the usual manner by adding active hydrogen compounds compatible with the system and/or destruction of the trimerization catalyst. All reaction runs are in styrene using HPMA and TDI. Reaction runs B through L were made using the procedure outlined in example 1 whereas reaction run A was made according to the procedure outlined in example 8. The procedure used for run A involves a somewhat different mode of addition of polyisocyanate than used in runs B through L and is used primarily for the synthesis of low concentration products.
TABLE I ______________________________________ Moles (NCO)- Moles (OH) Moles Trimerization Final Visc..sup.(1) Polyisocyanate % Styrene Temperature (.degree.C.) (cps) ______________________________________ A 1.26 75 30 998(22.4.degree. C.) B 1.16 70 45 395 C 1.20 70 45 10,000 D 1.10 60 55 370 E 1.22 50 55 17,000 F 1.10 50 55 2,200 G 1.10 50 25 1,050 H 1.00 50 75 790 I 1.00 50 55 450 J 0.95 40 55 1,400 K 0.91 40 55 800 L 0.97 30 55 66,000 ______________________________________ .sup.(1) Determined on a Brookfield Viscometer, Model LVT, #2 spindle, at 30 rpm. at 25.degree. C.
While it is essential that the isocyanurate compositions of this invention be based on one of the vinylidene carbonyl oxy alkanols defined above in order to obtain products having excellent high temperature properties, it is contemplated by the present invention that a minor amount of moieties derived from the vinylidene carbonyl oxy alkanols may be replaced with moieties derived from other monohydric alcohols, dihydric alcohols, monohydric phenols, or dihydric phenols. The saturated monohydric alcohols are especially useful with polyisocyanates of functionality greater than two. Although it has been found that the high temperature properties decrease as the amount of vinylidene carbonyl oxy alkanol decreases, one may be willing to sacrifice somewhat on the high temperature properties in order to introduce other desirable properties. For example, in some applications, one may be willing to sacrifice some high temperature properties for the inclusion of flame-retardancy or low smoke properties. The flame-retardance properties may be introduced by substituting a minor amount of the vinylidene carbonyl oxy alkanol with a phosphorus or florine, chlorine or bromine containing alcohol or phenol. Similarly, low smoke properties may be introduced by substituting a minor amount of the vinylidene carbonyl oxy alkanol with sulphur containing alcohols or phenols. While minor amount of any hydroxyl or phenolic material may be included in the isocyanurate compositions of this invention, it should be remembered that the isocyanurate compositions of this invention must be fusible and must meet the solubility test described above and must contain at least a major amount os isocyanurate moieties derived from a vinylidene carbonyl oxy alkanol described above.
Illustrative examples of monohydric alcohols and monohydric phenols which may be used to replace up to 49 mol percent of the vinylidene carbonyl oxy alkanols described above include: methanol, ethanol, propanol, butanol, isobutanol, octyl alcohol, cyclohexanol, benzyl alcohol, allyl alcohol, glycerol diallyl ether, trimethylolpropane diallyl ether, saturated halogenated alcohols, halogenated alcohols containing ethylenic unsaturation, for example, dibromoneopentyl glycol monoacrylate and monomethacrylate, halogenated allyl alcohols, monohydric alcohols such as 2-bromo ethanol, 3-bromo-1-propanol, 4-chloro-1-butanol, 2-chlorethanol, 4-chloro-1-hexanol, 3-chloro-1-propanol, 2,3-dibromo-1-propanol, 2,3-dichloro-1-propanol, 2,2,2-trichloroethanol, 1-bromo-2-propanol, 1-chloro-2-propanol, 1,3-dibromo-2-propanol, and 1,3-dichloro-2-propanol, mono acrylate and mono methacrylate esters of alkoxylated bisphenol A and alkoxylated tetra bromobisphenol A, and polyoxyethylene and polyoxypropylene ethers of monohydric phenols.
Illustrative examples of dihydric alcohols which may be used to replace up to 33 mol percent, and preferably up to 10 mol percent, of the vinylidene carbonyl oxy alkanols described above include: ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, compounds characterized by the formula: ##STR10## wherein R.sub.1 is an alkyl group containing from 1 to 4 carbon atoms, 1,4-butane diol, pentamethylene glycol, hexamethylene glycol, glycerol methyl ether, polyoxyethylene and polyoxypropylene ethers of dihydric phenols such as bisphenol A, glycerol monochlorohydrin, glyceryl monostearate, dihydroxy acetone, and monoesters of the above polyols and acrylic acid or methacrylic acid.
In general, phenols in small amounts (up to 20 mole percent) that are reactive with aromatic isocyanates may be used in the practice of this invention. When reactive phenols are used, it is particularly important that essentially all of the phenolic hydroxyl groups are reacted with isocyanate groups so that unreacted hydroxyl groups will not be available to interfere with subsequent free radical curing reactions. Phenols such as 4-hydroxyphenyl 4'-chlorophenyl sulfone are especially useful because they characteristically improve the fire retardant and smoke properties of the product while still retaining elevated temperature retention of physical properties. Phenol may also be used to block a minor portion of the isocyanate functionality which may later be regenerated at elevated temperatures to produce products with improved bonding to a substrate, especially glass fibers. Nitrophenols do not react readily with isocyanates and are not within the scope of this invention.
The unsaturated isocyanurate compositions of this invention may be homopolymerized or copolymerized with one or more other ethylenically unsaturated copolymerizable compounds. Where the unsaturated isocyanurate composition of this invention is to be copolymerized with a copolymerizable monomer, the isocyanurate composition may be dissolved in the copolymerizable monomer or it may be desirable to utilize the copolymerizable compound as a solvent for the reaction system in which the ethylenically unsaturated isocyanurate compositions of this invention are formed. If the ethylenically unsaturated copolymerizable monomer is to be used as a solvent for the preparation of the unsaturated isocyanurate products, the solvent should not contain any groups which would react with isocyanate groups or in any way interfere with the urethane formation reactions or trimerization reactions which occur in the formation of the isocyanurate products of this invention. Thus, the solvent should not contain any hydroxyl, carboxyl, or amine groups which might interfere with these reactions. This limits the suitable solvents to esters, ethers, hydrocarbons and similar solvents containing non-reactive groups. Illustrative examples of solvents which may be employed in the preparation of the isocyanurate products of this invention include: divinyl benzene, styrene, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, butyl acrylate, butyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, chlorostyrene, acrylonitrile, vinylidene chloride, vinyl acetate, vinyl stearate, vinyltolylene, hexanediol diacrylate, hexanediol dimethacrylate, tetrahydrofurfuryl methacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, allyl methacrylate, diallyl fumarate, tetramethylene glycol diacrylate, trimethylolpropane triacrylate, neopentyl glycol diacrylate, 1,3-butylene glycol diacrylate, 1,3-butylene glycol dimethacrylate, polyethylene glycol diacrylate, dimethylstyrene, ethylstyrene, propylstyrene, para-chloromethyl styrene, meta-dibromoethyl styrene, bromo styrene, dichloro styrene, t-butyl styrene, vinyl propionate, and vinyl butyrate. Nonpolymerizable solvents may also be used, for example, benzene, toluene, xylene, and ethylbenzene. The solvent may be removed from the reaction mixture after the formation of the isocyanurate to give a solid product. The solid product may be dissolved in the same or a different polymerizable solvent prior to curing. Mixtures of solvents may also be used. Preferred solvents are styrene, a mixture of styrene and methyl methacrylate, and a mixture of styrene and divinylbenzene.
When the isocyanurates of this invention are prepared in the absence of solvent, the product formed is a solid and requires special processing which permits the easy removal of the heat generated by the reaction and which prevents the reaction mixture from reaching high temperatures which may induce insolubility and gelation of the products. Among these special processing techniques may be the trimerization of the monourethane in thin layers on moving temperature-controlled belts or in temperature-controlled trays.
The amount of solvent employed to dissolve the isocyanurate compositions of this invention may vary over a very wide range. The particular amount of solvent used will depend somewhat on the nature of the solvent and on the solubility of the particular isocyanurate used. The polymeric character of the isocyanurate product allows maintenance of adequate working viscosity at relatively low concentrations of dissolved solids. Products of this invention may be made which permit adequate laminate working viscosity, which is defined as 100 to 1,000 centipoises Brookfield as determined on a Brookfield Viscometer, Model LVT, #2 spindle, at 30 rpm., at 25.degree. C. The amount of solvent will also depend on the nature of the properties desired in the final cured product. Thus, if one is interested in preparing a copolymer of styrene and an isocyanurate of a monourethane of tolylene diisocyanate and hydroxypropyl methacrylate, for example, the high temperature properties of the final product will increase as the concentration of the styrene decreases. In general, however, the amount of solvent used will be from 5 to 95 weight percent of the total composition and preferably from 30% to 80% by weight of the total composition. A particularly preferred concentration is about 50% by weight.
The unsaturated isocyanurate compositions prepared by the process of this invention and solutions thereof in copolymerizable solvent may be polymerized or cured in accordance with polymerization conditions conventional in the art for the polymerization of ethylenically unsaturated materials. Isocyanurates of this invention, particularly styrene solutions of isocyanurates made with tolylene diisocyanates or polymethylene polyphenylene polyisocyanate and hydroxyl propyl methacrylate, hydroxyl ethyl methacrylate, or hydroxyl propyl acrylate, are less sensitive to oxygen than conventional vinyl systems in yielding tack-free surfaces. In general, the polymerization may be carried out by reacting the unsaturated isocyanurate in the presence of a polymerization catalyst. Suitable polymerization initiators include the various peroxide initiators such as benzoyl peroxide, methyl ethyl ketone peroxide, di(2-ethylhexyl) peroxydicarbonate, t-butyl perbenzoate, dicumyl peroxide, and t-butyl hydroperoxide. Other polymerization catalysts which may be used include azo type initiators such as azobisisobutyronitrile. The amount of initiator employed is usually very small. For example, from about 1 part of initiator per 1000 parts of the polymerizable mixture to about 5 parts per 100 parts of said mixture.
In many applications, it is desirable to start the polymerization without the application of external heat. In such cases it is customary to add an accelerator to the system. Suitable accelerators include cobalt, manganese, lead, and iron compounds, such as cobalt naphthenate and manganese naphthenate, and tertiary amines such as dimethyl aniline.
The following are three illustrative examples of peroxide-promoter formulations which may be used to cure the unsaturated isocyanurates of this invention:
Formulation I
1% Benzoyl peroxide PA1 0.2% Dimethyl aniline PA1 0.02% Dimethyl aniline PA1 0.06% Cobalt naphthenate PA1 2.0% Methyl ethyl ketone peroxide PA1 0.03% Cobalt naphthenate PA1 0.5% Acetylacetone peroxide (4% active oxygen) PA1 1.5% t-butyl perbenzoate
Formulation II
Formulation III
In order to avoid premature polymerization of the isocyanurate composition of this invention, a small amount of a cupric salt such as cupric acetate, or a conventional polymerization inhibitor, such as hydroquinone, methyl ether of hydroquinone, phenothiazine, and tertiary butyl catechol, may be incorporated either into the reaction mixture prior to preparation of the isocyanurate product or into the final product or both.
The resulting isocyanurate product, particularly when prepared as a solution in a copolymerizable monomer, may contain any of the additives which are conventionally employed in polymerization systems, for example, antioxidants, U.V. absorbers, dyes and pigments.
The unsaturated isocyanurate products of this invention have been found to be particularly useful in applications such as castings, coatings, and laminates where it is desirable to have excellent flexural and tensile properties and good corrosion resistance at elevated temperatures. Laminates prepared with wettable fibers preferably contain at least 20% by weight of isocyanurate composition and up to 80% by weight of wettable fiber. Cured products obtained from polymerizing concentrated isocyanurate solutions of this invention exhibit thermal stability at temperatures above 325.degree. F.
The products of this invention may be used alone or in combination with other ethylenically unsaturated monomer compositions. In addition, these products may be used in combination with inorganic fillers, such as calcium carbonate, magnesium oxide, alumina trihydrate; organic polymers such as polyethylene, polymethylmethacrylate and other additives to reduce shrinkage; and fire retardant additives or other polymerizable resins, such as general purpose polyester resins. The products of this invention are especially useful when used in combination with glass fibers, cellulosic fibers, aramide fibers, or other fibers to produce reinforced structures, such as laminates and pipe. The products of this invention exhibit excellent wettability when used with these fibers.
The invention will be better understood from a consideration of the following examples which are presented for illustrative purposes and are not to be considered as defining or limiting the scope of this invention. All parts and percentages are by weight unless otherwise specified.
In the following examples, the castings and laminates are prepared as follows:
Castings are prepared by pouring the isocyanurate solution containing the curing reagents between two sheets of plate glass separated by a 1/8" polytetrafluoroethylene covered wire spacer. The curing reagents are added to the solution of isocyanurate in copolymerizable solvent by first adding the indicated promoter and accelerator to the isocyanurate solution and then adding the indicated peroxide. The casting is maintained at room temperature for 18-24 hours and then the resin is heated one hour at 100.degree. C. in an oven to undergo postcuring;
Laminates are prepared by rolling the indicated isocyanurate solution containing the curing reagents evenly onto glass fiber mats with a paint-type roller then rolling thoroughly with a grooved laminating roller. The curing reagents are added to the solution of isocyanurate in copolymerizable solvent by first adding the indicated promoter and accelerator to the isocyanurate solution and then adding the indicated peroxide. 1/8" thick laminates are prepared with two layers of split strand 11/2 ounce glass mats sandwiched between two 10 mil. surfacing "C" glass mats. The weight of the glass is 25% of the total resin glass weight. 1/4 inch thick laminates are made by the following combination of glass mats impregnated with resin: 10 mil. surfacing "C" glass mat, two layers of 11/2 ounce chopped strand mat, 1 layer woven roving, one layer of 11/2 ounce chopped strand mat, 1 layer of woven roving and a final layer of 11/2 ounce chopped strand glass mat. The amount of resin used to make this 1/4" laminate is adjusted to give a resin ratio of 70%. Laminates are covered with a thin polyester film to exclude air from the surface during cure. After 18-24 hours at room temperature the cured laminates are heated for 1 hour at 100.degree. C. in an oven for postcure.
Physical properties of the castings and laminates prepared in the following examples are measured by the indicated ASTM test methods:
______________________________________ Physical Property ASTM Test Method ______________________________________ Flexural strength D 790 Flexural modulus D 790 Tensile strength D 638 Tensile modulus D 638 % Elongation D 638 Izod Impact strength D 256 Barcol Hardness D 2583 Heat Deflection Temperature (264 psi) D 648 ______________________________________